Abstract P1-13-06: Exploring the real-life incidence of toxicities amongst obese breast cancer patients receiving adjuvant chemotherapy dosed based on absolute body weight

Abstract

Abstract Background: Obesity is an established risk factor for developing breast cancer and is also a negative prognostic indicator for higher recurrence risk.1 Adjuvant chemotherapy reduces the likelihood of metastatic recurrence and improves disease-free and overall survival.2 However, the practice of optimal dosing of adjuvant breast cancer chemotherapy amongst obese patients remains contentious with concerns regarding excessive toxicity if obese patients are dosed based on actual body weight (ABW).2-4 A 2014 study reported that obese patients were five times more likely to have dose reductions in cycle 1 than non-obese patients.5 Inadequate dosing amongst obese breast cancer patients may have deleterious implications on ultimate prognosis.2-4 This study aimed to investigate whether chemotherapy dosing using ABW in obese breast cancer patients is associated with comparable incidences of toxicity. Methods: A retrospective cross-sectional study was conducted amongst 257 patients (aged ≥18) treated in the adjuvant setting with doxorubicin-cyclophosphamide-paclitaxel (AC-P) or docetaxel-cyclophosphamide (TC) with/without trastuzumab between 2014 and 2017. Obesity was classified as a body mass index (BMI) of ≥30, with morbid obesity defined as a BMI≥35. Chemotherapy dosing based on body surface area calculated using ABW was considered the standard protocol with any variations from this dosing method for cycle 1 being recorded. Subsequent dose adjustments were also noted. The primary outcome was tolerability of chemotherapy regimens dosed using ABW with outcome measures of toxicity defined as the incidence of febrile neutropaenia, the incidence of grade 3 or 4 non-haematological toxicities and the number of hospitalisations during the treatment course. Results: 257 patients were eligible (1 male, 256 females). Median age was 55 (range, 31-78). AC-P was the most commonly used regimen (48.6%), followed by TC (40.1%). Obesity and morbid obesity were noted amongst 17.9% and 15.6% of patients respectively; with 63.8% with a BMI≥25. Chemotherapy dosing was largely based on ABW, with only 4.3% of patients dosed based on ABW or had their dosing body surface area capped at 2.0m2. In patients with a BMI≥25, 25% had febrile neutropaenia compared to 21.8% in those with normal BMI (p=0.58). Incidence of febrile neutropaenia during treatment by BMI – underweight: 33.3% (p=0.61); normal: 24.1%; overweight: 24.4% (p=0.97); obese: 17.4% (p=0.37); morbidly obese: 25%(p=0.92). Grade 3-4 non-haematological toxicities had comparable incidences between the normal BMI group as opposed to the overweight/obese group (23.0% vs 18.9% respectively, p=0.44). Hospitalisations by BMI - underweight: 50% (p=0.85); normal BMI: 46%; overweight: 42.3% (p=0.64); obese: 54.3%(p=0.36); morbidly obese: 57.5%(p=0.23). Conclusion: This study demonstrates that obese breast cancer patients do not experience higher toxicities when their adjuvant chemotherapy is dosed based on ABW. This supports current guidelines for dosing amongst obese patients. Citation Format: Tam LL, Mcguigan B, Connor A, Allan S, Sanmugarajah J. Exploring the real-life incidence of toxicities amongst obese breast cancer patients receiving adjuvant chemotherapy dosed based on absolute body weight [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P1-13-06.